This invention concerns construction of miniature x-ray tubes. In particular the invention is directed at an efficient and rugged connection of a high voltage cathode filament lead to an extractor cup which helps shape the path of electrons from the cathode in such an x-ray tube.
Miniature x-ray tubes, generally of the size and configuration contemplated in this invention, are shown in Xoft Microtube U.S. Pat. No. 6,319,188, and also in U.S. Pat. Nos. 5,854,822 and 5,621,780. Also, Xoft Microtube pending application No. 10/397,498 describes a cathode assembly with a cathode manufactured by MEMS technology and discloses a means of forming an extractor cup and electrically connecting the extractor cup to high voltage.
As is known, an extractor cup is usually needed to help focus and direct the stream of electrons leaving a cathode en route to the anode in an x-ray tube, and the need for focusing this electron beam typically becomes more acute in the case of miniature x-ray tubes. However, the connection of an extractor cup to high voltage, in a rugged, reliable and feasibly manufacturable manner, presents something of a challenge. There are problems of reliably connecting a conductor to one end of a cathode filament or a wire lead to the cathode; it is not feasible simply to extend a conductor wire through the tube wall to the exterior, because of sealing problems and because of the requirement to isolate this HV from the tube exterior which is at ground potential; and in miniature size, which may be down to about 1 mm in tube diameter, the options are limited in making secure high voltage connections in proper alignment, to withstand high temperature, without causing the tube to fail ultimately through arcing and while still obtaining a rugged and reliable connection of the extractor cup to a base of the cathode and secure connection of the cathode itself to the base.